This application claims priority of European Patent Application No. 99305516.9, which was filed on Jul. 12, 1999.
1. Field of the Invention
This invention relates to a Universal Mobile Telephone System (UMTS) network and more especially to a method of calculating the number of bits to be punctured or repeated to achieve effective rate matching.
2. Description of the Prior Art
In a UMTS system, the technique of time multiplexing is used to combine different services required by one user. The services have different Quality of Service (QoS) requirements, such as signal power with respect to noise and interference power, and latency restrictions which lead to different requirements of transmission power; transmission power must therefore be adjusted so that in any one transmission channel the QoS is maintained for the service making the highest demand, but simultaneously transmission power is minimised.
To achieve this, and also to adapt the symbol data rate to the physical channel data rate, the method of rate matching is used, ie, some bits are punctured or repeated. The principle of rate matching is described by the Ericsson company in the paper xe2x80x9cDescription of Rate Matching in UTRA/FDD,xe2x80x9d TDoc SMG2 UMTS L1 235/98 and by the Nokia company in the paper xe2x80x9cMapping Rule for semi static rate matching,xe2x80x9d TDoc SMG2 UMTS L1 476/98. The publication by Nokia also proposes a method of deriving the number of bits to be punctured or repeated to achieve the required QoS for two different services by interpolation methods. However, interpolation cannot be applied to more than two services, which is a substantial limitation on the network and also the algorithm is complex.
According to the invention, in a UMTS network in which a plurality of services of a single user having different transmission power requirements are multiplexed in one channel and the technique of rate matching is applied, a method of determining for each service the number of bits to be punctured or repeated characterised by the steps of
deriving for each service the Energy per Bit per Noise density EB/NO required to achieve a desired Bit Error Rate;
from each EB/NO deriving a value of the Energy per coded Symbol per Noise density ES/NO;
and from ES/NO deriving a rate matching factor by which that ES/NO can be matched to the minimum Energy per coded Symbol per Noise density applicable to said one channel.